The present invention relates to an EDM apparatus and more particularly to a travelling wire EDM apparatus wherein a workpiece is cut, by electrical discharges, by means of an electrode tool in the form of a wire.
In EDM apparatus of that type, the travelling wire electrode is supported by a pair of guide members each mounted on the end of a support arm and disposed one on one side and the other on the other side of the machining zone. A pair of servo motors displace the pair of wire guide members relative to the workpiece according to a predetermined path for the cut in the workpiece, and an additional pair of servo motors may be used for displacing the wire guide members relative to each other, such as to provide the active portion of the electrode wire with a predetermined inclination relative to the workpiece in the course of a cutting operation.
Means are known for disposing the active portion of electrode wire at an angle relative to the cutting path plane, such means consisting in effecting a relative displacement between the wire guide members either in polar co-ordinates, for example by means of eccentrically rotating devices, or in cartesian or planar co-ordinates by means of cross-slides mounted on the end of one of the arms supporting a wire guide member.
The known methods and systems present the inconveniences of lacking in precision because the displacement of the wire guide members is the resultant of two super-imposed displacements, resulting in backlash, loss of rigidity and compounding of errors. In addition, the mechanism mounted on the end of one of the support arms is voluminous and leads to a machine design which is more complex and more costly.
The present invention eliminates the inconveniences of the prior art and provides an apparatus in which one of the electrode wire guide members is displaced on one of the support arms in one direction, and the other guide member is displaced on its support arm in an other direction.